1. Field of the Invention
The present invention relates to a heat gun and, particularly, to a heat gun having improved flow effects.
2. Description of the Related Art
EP 1795803 A2 shows a modular gas burning hand tool including a main body, an ignite gas pipe for circulating gas defined by the main body which extends longitudinally, a grip handle, and a burner part including a hollow body extending from the main body and communicating with the ignite gas pipe and including a gas-powered unit disposed at an end of the hollow body. The burner part has a junction part, the main body has a junction part, and the junction parts are adapted to be releasably secured to one another.
It is known for gas heat guns to use high pressure gas and to incorporate venturi tubes to mix gas. The high pressure gas is spewed at a high velocity out of a gas nozzle in the venturi tube, which causes outside air to flow to the venturi tube and a chamber from which a flame exits to achieve an appropriate ratio of gas mixture and to increase the amount of the gas mixture. Furthermore, the venturi tube includes an opposite end nconnecting to a mixing chamber. Moreover, the mixing chamber is shrouded by a flow-rectifying cover that is configured to control the flow speed and distributability of the gas mixture as well as preventing the backward propagation of the flame.
An ideal high power gas heat gun is required to provide a high speed flame. In this regard, a user can aim the gas heat gun at a target to be heated easily. Moreover, the greater the width of a flame exit end of the gas heat gun, the easier the user can operate the gas heat gun to heat the target precisely and to heat large areas quickly. However, conventional high power gas heat guns suffer problems, including:
1. A flame flowing out of the flame exit end is not evenly distributed and therefore doesn't apply heat to a surface evenly.
2. Mixing and dispensing gas unevenly result in poor combustion, which not only reduces efficiency and wastes gas, but which also produce too much noxious carbon monoxide (CO) and nitrogen oxide (NOx).
3. The temperature of the flame exit end is very high, and a large amount of heat is concentrated. Furthermore, heat radiates and conducts. The chamber, which includes the flame exit end, is hot and often reaches a temperature above 100 degrees Centigrade. Therefore, there is a high risk that the user gets burned inadvertently.
4. The flow-rectifying cover has an exit being too small, which results in substantial pressure losses, a flow capacity decrease overall, and a difficulty to increase heat power.
5. High pressure gas and the gas mixture create turbulence in the mixing chamber and the flow-rectifying cover and result in a noise.
6. Rectifying flows unduly cause the flame at the flame exit end to flow at a low speed. Since the flame spreads linearly mostly, if the flame flows at a speed which is too low, the flame is susceptible to distortion under thermal buoyant effects. Thus, it is difficult to aim the gas heat gun at the target precisely. The flame is also easily affected by air currents when the gas heat gun is used in an outside environment. Thus, it is difficult to operate and aim the gas heat gun at the target precisely in a wind environment and especially if the wind varies directions. Furthermore, when the flame moves against the wind, the flame, which flows too slow, may burn backward toward the user.
7. If gas is mixed and dispensed unsteadily, a suitable pressure range for supplying gas becomes limited, and the chance to ignite the gas is substantially reduced.
The conventional mixing chamber is fan-shaped and varies regularly in cross section along a center axis of the venturi tube. In order to speed up operations, it is necessary that areas that can be heated instantaneously and that heat power are increased. Thus, an exit of the mixing chamber which has a narrow width is not desired. Increasing the width of the exit of the mixing chamber, however, makes it more difficult to control flows at the exit at the same speed. In fact, flows at two sides of the exit flow faster, and flows in the middle of the exit flow slower (see FIG. 12). If reducing the width of the exit of the mixing chamber, areas that can be heated are smaller. If increasing heat power, heat concentrates in a small region and results in local overheating. If increasing a distance between the gas heat gun and the target, thermal buoyant force and air flow disturbance make it difficult for the user to aim the gas heat gun at areas to be heated. Therefore, a high power gas heat gun that allows a user to heat a target precisely and evenly includes a wide flame exit and a flame that exits at high speed.
In addition to flow noise and the phenomenon that the temperature at the two sides are higher, the flame is nearly transparent. Therefore, it is hard to perceive the direction of heat transfer. This causes the user to have a poor aim of the target and where the gas heat gun aims is not exactly where the user wants to heat. Furthermore, since the flows are not at the same speed, an increase of heat capacity results in incomplete combustions at the two sides, and trying to use flow guides to control flows, however, imposes frictional forces on the flows and reduces overall flow capacity and efficiency.
Since a large amount of heat is concentrated at the flame exit end, the temperature is very high, due to heat radiation and conduction, and is often above 100 Centigrade. Therefore, there is a high risk that the user gets burned inadvertently. After the flame stops, it also takes quite a while to dissipate heat and cool the temperature down with respect to the ambient temperature, and since the user doesn't know when the gas heat gun has cooled, it is easy that he or she can get burned inadvertently.
FIG. 11 is a partial, cross-sectional view of a conventional gas heat gun. As set forth, the gas heat gun includes a device 11′ from which gas burns. The device 11′ includes a net and a main body defining a tube in circular cross-section. When gas flows in the tube, it flows faster in the center of the tube than at the edges of the tube. The gas will flow out of tube and into a burner part 9′. Likewise, the gas flows faster in the center of the burner part 9′ than at edges of the burner part 9′. The gas in the burner part 9′ will contact the device 11′. The device 11′ will obstruct and deflect the gas. FIG. 11 shows that after the gas is obstructed by the device 11′, it is partially deflected and flows toward two sides of the burner part 9′ in opposing directions. Consequently, flow capacity at the two sides of the burner part 9′ is more, and flow capacity in the middle of the burner part 9′ is lesser. As a result, the temperature at the two sides is higher than the temperature in the middle, and the gas heat gun does not give out even heat and uniform temperature. Furthermore, the temperature of the burner part 9′ is very hot, but the user can't tell by appearance. Therefore, it is easy that he or she can get burned inadvertently.
The present invention is, therefore, intended to obviate or at least alleviate the problems encountered in the prior art.